The present invention relates generally to implantable medical devices and in particular to an implantable transvenous catheter as well as an analysis, pacemaker and/or defibrillation unit.
A disorder having a rapid, irregular sequence of heart beats resulting from a disordered electrical excitation of the atria, is known as atrial fibrillation or atrial flutter. A distinction is made between paroxysmal (sudden) and persistent (chronic) arrhythmia. Some of these arrhythmia types may be treated by medications while others must be treated by external cardioversion. For this latter treatment, a high quantity of energy is output through the external area of the body, conventionally under anesthetic to restore the normal cardiac rhythm (sinus rhythm). Several studies have managed to show that the transvenous cardioversion of atrial fibrillation and/or atrial flutter can be performed with a considerably lower energy level than if the energy is applied to the external area of the body.
The use of an energy quantity of 200 J in an initial phase of treatment for external cardioversion and, in the event of its failure, two further pulses of 360 J, is proposed by Gordon A. Ewy as the optimal form of therapy in his article entitled xe2x80x9cOptimal Technique for Electrical Cardioversion of Atrial Fibrillationxe2x80x9d, Circulation, pp. 1645 ff, Volume 86, No. 5, November 1986. Despite these high levels of energy output, Ewy emphasizes that great care must be given to ensuring the correct positioning and low transfer resistance of the external defibrillation electrodes, to achieve the best results.
As part of a comparative study, Lxc3xa9vy et al. report in their publication entitled xe2x80x9cA Randomized Comparison of External and Internal Cardioversion of Chronic Atrial Fibrillationxe2x80x9d on the results of external and internal cardioversion and come to the conclusion that internal cardioversion is more effective for the restoration of the sinus rhythm without involving any increased risks. Internal cardioversion was completed for this study using a catheter fitted with an electrode together with an external thorax electrode.
E. Alt, C. Schmitt, R. Ammer, M. Coenen, P. Fotuhi, M. Karch and R. Blasini present a method of therapy for treating arrhythmia in their article entitled xe2x80x9cInitial Experience with Intracardiac Atrial Defibrillation in Patients with Chronic Atrial Fibrillationxe2x80x9d, PACE, Volume 17, May 1994, Part II, in which an initial catheter fitted with a distal electrode is inserted in the Coronary Sinus in a catheter laboratory with X-ray monitoring, and a second catheter, also fitted with a distal electrode, is positioned in the right atrium. With this form of therapy, too, low levels of energy were used to remedy both spontaneous as well as induced atrial fibrillation, essentially with no negative effects.
Although the transvenous forms of therapy are not only far superior in terms of the levels of output energy compared to methods which use externally applied electrodes, there have been major effects to achieve further improvements in the therapy and in the equipment used for it.
A process of this nature in clinical emergency should provide extremely short preparation times and place as little stress as possible on the patient. Furthermore, the safety involved with this type of therapy should be increased. Although costs are of lesser importance in this particular area, they are becoming increasingly significant recently as a result of the wide range of efforts to make savings.
Using the transvenous catheter proposed by the invention, it is now possible to perform both defibrillation and the detection and stimulation to correct abnormal cardiac functioning, such as arrhythmias, essentially using a single catheter. The catheter, also known in clinical practice as a xe2x80x9csingle electrode,xe2x80x9d can be inserted into the heart quickly and safely, for example by means of puncturing a vein. In initial applications, the catheter proposed by the invention was positioned correctly with an X-ray exposure time of, on average, 4.8 to 5.5 minutes and then started. By further practice and with additional experience, it is assumed that these times can be reduced to a range from one to three minutes, so that both for intensive medical, operative and post-operative emergency situations, rapid initial care can be ensured.
It should also be emphasized that the invention proposes that the catheter can be inserted and correctly positioned by a single operator so that the interaction of several operators for the coordinated positioning of several electrodes is not necessary.
Another particular advantage of the catheter proposed by the invention is that adequate spacing between the electrodes is also ensured as a result of the axial spacing of a proximal electrode from a distal electrode to ensure that the interaction length does not fall below the minimum for the treatment. The axial spacing can be adjusted by means of producing a defibrillation axis which is ideal for the atrium, namely between the right-hand atrium and the coronary sinus. The catheter proposed by the invention stabilizes this position by means of its longitudinal structure which means that essentially no further means of fastening are required to hook the electrodes into the tissue, but such means may be used if desired.
Even in a floating mode, without direct tissue contact, it may always be assumed that the catheter proposed by the invention will not suffer a short circuit as a result of the axial spacing of the electrodes and that detection, stimulation and cardioversion or defibrillation can always be performed safely.
Both psychologically and physically the catheter proposed by the invention presents considerably less stress for the patient. Only a single incision is required and the temporal and medication stress is also less.
One embodiment of the present invention is a disposable catheter to reduce cost.
In one embodiment, the distal electrode and proximal electrode positioned in the electrically active section of the catheter has a spacing of between 10 and 100 mm between each other. This means that consideration may be given on the one hand to the size of the heart and on the other to the symptoms of the individual case. In this embodiment, the axial spacing is around 85 mm.
Spiral electrodes have proved to be particularly beneficial for use as the proximal and distal electrodes. This electrode design offers a high level of flexibility, good position-retaining characteristics and a large electrical interaction area. This means that it was possible with a proximal electrode just 55 mm in length and a distal electrode just 45 mm in length to create an electrically active overall area of 1040 mm2. Compared to the levels of energy used with conventional treatments of 200 to 300 Joules per defibrillation process, it was possible to achieve reliable defibrillation using the device proposed by the invention with an energy level of just 1 to 8 Joules. Even when used on patients who are resistant to external cardioversion, it was possible to remedy atrial flutter with an output energy level of 2 to 20 Joules.
With a ring electrode positioned between the proximal and distal electrodes, it is also possible to monitor and analyze and stimulate the heart activity at the same time as and/or at a different time to the electrically active conditions.
The electrically passive section of the catheter, in one embodiment, consists of external electrical connections at the end away from the heart which can be used to connect an external heart pacemaker, an analysis and/or defibrillation unit. This means that the equipment which already exists in a hospital can continue to be used.
In particular, fluid-sealed electrical connections can be used with implantable units in the manner proposed by the invention.
In another embodiment, on the proximal end of the electrically active section of the catheter, there is a cap at a spacing from the distal electrode. This provides the correct axial spacing of the distal electrode, in particular, from the base of the right-hand atrium, and also allows the electrodes to be secured in position. In one embodiment, the cap is a blind cap.
If the cap is designed in the form of a further electrode, the monitoring and analysis functions as well as the stimulation of the heart can be performed from a remote point. The electrical activity may be recorded and evaluated at least in two sections. Furthermore, the proximal and/or the distal electrode may be split into separate areas and alternatively or additionally fitted with electrical cables and connectors to allow even better monitoring and analysis as well as extended forms of therapy.
The catheter proposed by the invention may be inserted in a particularly simple manner if a stylet duct extends over the length of the catheter and is fitted with a malleable stylet wire. The stylet wire can be moved axially within the stylet duct and is a flexible metallic rod or wire which can retain a desired imparted shape and is inserted in the stylet duct of the catheter to stiffen it and give it form during its passage through the vasculature.
It should be pointed out that in the sense proposed by the invention, the term xe2x80x9ccatheterxe2x80x9d refers not only to a probe which is inserted for a limited period which is fitted with electrical connectors and contacts, but also any form of chronic or permanently implanted probe of that nature with electrically controllable electrodes and the relevant connectors. Furthermore, the term xe2x80x9canalysisxe2x80x9d in conjunction with the invention is intended to comprise the functions of monitoring, recording, storing, evaluation and/or transferring data to additional function modules from implanted or external units.